In many instances the best or only way to move a vehicle to a particular destination is via a railway track. This may be because the railway offers a smoother surface than paved roads, or because the railroad track is the only available cleared surface that reaches a particular destination. In addition, railway maintenance vehicles are often expected or required to travel on both roads and railway tracks, and require means for converting from one travel surface to the other. Most surface vehicles designed for use on paved roads and for use off-road are not suitable for use on a railway. As the railway is made up of two parallel steel tracks supported by spaced cross ties, and the typical lateral distance between the wheels of most surface vehicles is different than the spacing of the parallel railroad tracks, the road wheels cannot stably ride upon the railway but instead usually have to ride over the spaced apart cross ties, which places enormous demands on the vehicle suspension.
It is known in the art to provide an apparatus for converting road vehicles for railway travel. Examples of such vehicles are disclosed in U.S. Pat. Nos. 4,077,328; 804,025 and 3,730,105. Such a conversion apparatus typically includes railway wheels movably mounted to the frame of the vehicle for movement between a raised, retracted position for road travel and a lowered, distended position for rail travel. A drawback to this arrangement has been the lack of suitable suspension means interposed between the vehicle frame and the railway tracks, resulting in a harsh ride. Also, when the railroad wheels support the vehicle, the road wheels tend to extend downwardly toward the track which sometimes causes the road wheels to engage other objects and interfere with the movements of the vehicle on the railroad tracks.
This problem has been addressed in the art by mounting the conversion apparatus at one point to the vehicle suspension and at another point the vehicle frame to transmit some of the load of the vehicle through the vehicle's own suspension to provide some cushioning of the ride along the railway. For example, U.S. Pat. No. 4,488,494 teaches a conversion apparatus in which a support arm is pivotally attached at one of its ends to the vehicle frame and is pivotally attached at its opposite end to the vehicle suspension. A railway wheel support plate carries a railway wheel and is pivotally mounted to the support, arm.
While arrangements of this general type provide a more cushioned ride through the use of the vehicle road wheel suspension to partially support the railroad wheels, it does so at the expense of decreased service life of various components of both the vehicle road wheel suspension and the conversion apparatus. This is so because the arcuate path of travel of the end of the pivoted support arm which is attached at one end to the vehicle suspension and pivots at its other end about the vehicle frame does not match the designed path of travel of the suspension apparatus of the vehicle road wheels. Therefore, as the vehicle suspension moves up and down, and as the support arm of the conversion apparatus pivots, longitudinal stresses are placed on some components of the vehicle suspension as well as on some components of the conversion apparatus, which ultimately damage or shorten the life thereof. These unwanted stresses result both when the vehicle is driven over the road and when the vehicle is driven on the railway because the conversion apparatus is permanently attached to the vehicle road wheel suspension, regardless of the use of the vehicle.
Accordingly, it is seen that a need yet remains for an apparatus for converting road vehicles for railway travel which utilizes the suspension of the vehicle road wheels to provide a cushioned ride to the railroad wheels without damaging the suspension or diminishing the service life thereof. It is the provision of such an improved vehicle and the conversion apparatus therefore that the present invention is primarily directed.